Apparatus and method for transmitting wireless power

ABSTRACT

A method and apparatus are provided for determining, by a wireless power transmitter, whether a wireless power receiver is removed from a wireless power network managed by the wireless power transmitter. The method includes transmitting a command signal to report power information of the wireless power receiver at stated periods; determining whether a report signal corresponding to the command signal is received from the wireless power receiver; and determining that the wireless power receiver is removed from the wireless power network, if the report signal is not received after transmitting the command signal a predetermined number of times at the stated periods.

PRIORITY

This application is a Continuation Application of U.S. patentapplication Ser. No. 15/704,768, which was filed in the U.S. Patent andTrademark Office on Sep. 14, 2017, which is a Continuation Applicationof U.S. patent application Ser. No. 14/657,670, which was filed in theU.S. Patent and Trademark Office on Mar. 13, 2015, and issued as U.S.Pat. No. 9,806,537 on Oct. 31, 2017, which is a Divisional Applicationof U.S. patent application Ser. No. 13/717,273, which was filed in theU.S. Patent and Trademark Office on Dec. 17, 2012, and issued as U.S.Pat. No. 9,425,626 on Aug. 23, 2016, and claims priority under 35 U.S.C.§ 119(e) to U.S. Provisional Patent Application Ser. No. 61/576,050,which was filed in the U.S. Patent and Trademark Office on Dec. 15,2011, and under 35 U.S.C. § 119(a) to Korean Patent Application SerialNo. 10-2012-0089759, which was filed in the Korean Intellectual PropertyOffice on Aug. 16, 2012, the content of each of which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to a method and apparatus fortransmitting wireless power, and more particularly, to method andapparatus for recognizing wireless power receivers and transmittingwireless power thereto.

2. Description of the Related Art

Recently, wireless or non-contact charging technologies have beendeveloped, which are now widely used for a variety of electronicdevices, such as wireless electric toothbrushes or wireless electricshavers.

Using wireless charging technology, which is based on wireless powertransmission and reception, a battery of an electronic device, such as amobile phone, may be automatically recharged if, for example, a usersimply places the mobile phone on a charging pad without connecting aseparate charging connector to the mobile phone.

Wireless charging technologies may be roughly classified into acoil-based electromagnetic induction scheme, a resonant scheme, and aRadio Frequency (RF)/microwave radiation scheme, which deliverselectrical energy by converting it into microwaves.

Although the electromagnetic induction scheme has been used more often,recently, experiments using an RF/microwave radiation scheme have beensuccessful. Thus, it is expected that in the near future, more types ofelectronic products will be recharged wirelessly.

The electromagnetic induction-based power transmission transmits powerbetween a primary coil and a secondary coil. For example, an inducedcurrent occurs, when a magnet is moved around a coil. Using thisprinciple, a transmitter generates a magnetic field, and in a receiver,a current is induced depending on a change in magnetic field, therebyproducing energy. This power transmission method has excellent energytransmission efficiency.

As for the resonant scheme, power can be wirelessly transferred to anelectronic device by using the Coupled Mode Theory, even though theelectronic device is located several meters away from a charging device.The resonant scheme is based on a physics concept, wherein if a tuningfork rings, a nearby wine glass may also ring at the same frequency.However, the resonant scheme resonates electromagnetic waves containingelectrical energy, instead of resonating sounds. The resonatedelectrical energy is directly delivered only to devices having the sameresonant frequency, and any unused portion is reabsorbed aselectromagnetic fields instead of being spread into the air. Thus,unlike other electromagnetic waves, the resonated electrical energyshould not affect adjacent devices and a human body.

Although wireless charging schemes are garnering a great deal ofattention and research, no standard has been proposed for the priorityof wireless charging, a search for a wireless power transmitter andreceiver, a selection of a communication frequency between the wirelesspower transmitter and receiver, an adjustment of wireless power, aselection of matching circuits, and a distribution of communication timefor each wireless power receiver in one charging cycle. In particular, astandard is required for a wireless power transmitter to determineaddition and removal of a wireless power receiver to and from a wirelesspower network managed by the wireless power transmitter.

SUMMARY OF THE INVENTION

Accordingly, the present invention is designed to address at least theproblems and/or disadvantages described above and to provide at leastthe advantages described below.

An aspect of the present invention is to provide a standard for anoverall operation of a wireless power transmitter and receiver.

Another aspect of the present invention is to provide a method andwireless power transmitter for detecting a wireless power receiver, andtransmitting wireless power thereto.

In accordance with an aspect of the present invention, a method isprovided for controlling a wireless power transmitter, with the methodincluding periodically outputting a first power for detecting a loadvariation; based on detecting a first load variation caused by placementof a wireless power receiver within the wireless power transmitter whileoutputting the first power, continuously outputting a second power forcommunicating with the wireless power receiver; detecting a system errorwhile outputting the second power; based on detecting the system error,providing an indication regarding the system error and periodicallyoutputting the first power for detecting the load variation; anddetecting a second load variation indicating that the wireless powerreceiver is removed from the wireless power transmitter.

In accordance with another aspect of the present invention, a wirelesspower transmitter is provided that includes a power transmitter and acontroller, which is configured to control periodically outputting afirst power for detecting a load variation; based on detecting a firstload variation caused by placement of a wireless power receiver withinthe wireless power transmitter while outputting the first power, controlcontinuously outputting a second power for communicating with thewireless power receiver; detect a system error while outputting thesecond power; based on detecting the system error, provide an indicationregarding the system error and control periodically output the firstpower for detecting the load variation; and detect a second loadvariation indicating that the wireless power receiver is removed fromthe wireless power transmitter.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present invention will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 illustrates a wireless charging system according to an embodimentof the present invention;

FIG. 2A is a block diagram illustrating a wireless power transmitter anda wireless power receiver according to an embodiment of the presentinvention;

FIG. 2B is a block diagram illustrating a wireless power receiveraccording to an embodiment of the present invention;

FIG. 3 is a flowchart illustrating a method in wireless powertransmitter and receiver according to an embodiment of the presentinvention;

FIG. 4A is a circuit diagram illustrating a wireless power transmitteraccording to an embodiment of the present invention;

FIGS. 4B and 4C are graphs illustrating a current and a voltage,respectively, which are measured in the wireless power transmitter overtime, according to embodiments of the present invention;

FIG. 4D is a graph illustrating a temperature measured at one point of awireless power transmitter over time, according to an embodiment of thepresent invention;

FIG. 4E is a graph illustrating a phase at one point of a wireless powertransmitter according to an embodiment of the present invention;

FIG. 5 is a timing diagram illustrating load detection and signaltransmission in a wireless power transmitter according to an embodimentof the present invention;

FIGS. 6A and 6B are timing diagrams illustrating a power supplyoperation between a wireless power transmitter and a wireless powerreceiver according to an embodiment of the present invention;

FIG. 7 is a flowchart illustrating a method in a wireless powertransmitter according to an embodiment of the present invention;

FIGS. 8A and 8B are timing diagrams illustrating an operation wherein awireless power receiver fails to join a wireless power network managedby a wireless power transmitter, according to an embodiment of thepresent invention;

FIGS. 9A and 9B are timing diagrams illustrating an operation fordetermining to remove a wireless power receiver from a wireless powernetwork managed by a wireless power transmitter according to anembodiment of the present invention;

FIGS. 10A and 10B are timing diagrams illustrating communicationsignaling between a wireless power transmitter and a wireless powerreceiver according to an embodiment of the present invention; and

FIG. 11 illustrates an example of a device control table according to anembodiment of the present invention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features and structures.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will now be described indetail with reference to the accompanying drawings. In the followingdescription, specific details such as detailed configuration andcomponents are merely provided to assist the overall understanding ofthese embodiments of the present invention. Therefore, it should beapparent to those skilled in the art that various changes andmodifications of the embodiments described herein can be made withoutdeparting from the scope and spirit of present the invention. Inaddition, descriptions of well-known functions and constructions areomitted for clarity and conciseness.

FIG. 1 illustrates a wireless charging system according to an embodimentof the present invention.

Referring to FIG. 1, the wireless charging system includes a wirelesspower transmitter 100 and wireless power receivers 110-1, 110-2, and110-n. The wireless power transmitter 100 wirelessly transmits power1-1, 1-2, and 1-n to the wireless power receivers 110-1, 110-2, and110-n, respectively. More specifically, the wireless power transmitter100 wirelessly transmits the power 1-1, 1-2, and 1-n only to thewireless power receivers that are authorized by performing apredetermined authentication procedure.

The wireless power transmitter 100 forms electrical connections with thewireless power receivers 110-1, 110-2 and 110-n. For example, thewireless power transmitter 100 transmits wireless power in the form ofan electromagnetic wave to the wireless power receivers 110-1, 110-2,and 110-n.

Additionally, the wireless power transmitter 100 performs bi-directionalcommunication with the wireless power receivers 110-1, 110-2, and 110-n.The wireless power transmitter 100 and the wireless power receivers110-1, 110-2, and 110-n process and exchange packets 2-1, 2-2, and 2-n,each configured in a predetermined frame. The wireless power receivers110-1, 110-2, and 110-n may be implemented as, for example, mobilecommunication terminals, Personal Digital Assistants (PDAs), a PersonalMultimedia Players (PMPs), smart phones, etc.

The wireless power transmitter 100 wirelessly supplies power to thewireless power receivers 110-1, 110-2, and 110-n using the resonantscheme. When the wireless power transmitter 100 uses the resonantscheme, the distance between the wireless power transmitter 100 and thewireless power receivers 110-1, 110-2, and 110-n may be preferably 30 mor less. However, when the wireless power transmitter 100 uses theelectromagnetic induction scheme, the distance between the wirelesspower transmitter 100 and the wireless power receivers 110-1, 110-2, and110-n may be preferably 10 cm or less.

The wireless power receivers 110-1, 110-2, and 110-n charge a batterymounted therein by receiving wireless power from the wireless powertransmitter 100. Further, the wireless power receivers 110-1, 110-2 and110-n may transmit, to the wireless power transmitter 100, a signalrequesting the transmission of the wireless power, information forreceiving the wireless power, status information of the wireless powerreceiver, control information for the wireless power transmitter 100,etc.

The wireless power receivers 110-1, 110-2, and 110-n may send a messageindicating their charging status to the wireless power transmitter 100.

The wireless power transmitter 100 may include a display that displays astatus of each of the wireless power receivers 110-1, 110-2, and 110-n,based on the messages received from the wireless power receivers 110-1,110-2, and 110-n. In addition, the wireless power transmitter 100 maydisplay an estimated time remaining until the wireless power receivers110-1, 110-2, and 110-n will be fully charged.

Further, the wireless power transmitter 100 may transmit a controlsignal for disabling the wireless charging function of the wirelesspower receivers 110-1, 110-2, and 110-n. Basically, upon receiving thedisable control signal for the wireless charging function from thewireless power transmitter 100, a wireless power receiver will disablethe wireless charging function.

FIG. 2A is a block diagram illustrating a wireless power transmitter anda wireless power receiver according to an embodiment of the presentinvention.

Referring to FIG. 2A, the wireless power transmitter 200 includes apower transmitter 211, a controller 212, and a communication unit 213.The wireless power receiver 250 includes a power receiver 251, acontroller 252, and a communication unit 253. Herein, the term “unit”refers to a hardware device or a combination of hardware and software.

The power transmitter 211 wirelessly supplies power to the wirelesspower receiver 250 via the power receiver 251. The power transmitter 211supplies power in an Alternating Current (AC) waveform. However, whenthe power transmitter 211 receives power in a Direct Current (DC)waveform, e.g., from a battery, the power transmitter 211 supplies powerin an AC waveform, after converting the DC waveform into the AC waveformusing an inverter. The power transmitter 211 may be implemented as abuilt-in battery, or may be implemented as a power receiving interface,which receives power from an outside source, e.g., an outlet, andsupplies it to other components. It will be understood by those ofordinary skill in the art that the power transmitter 211 has no limit aslong as it is capable of supplying power in an AC waveform.

Additionally, the power transmitter 211 may provide AC waveforms to thewireless power receiver 250 in the form of an electromagnetic wave.Accordingly, the power transmitter 211 may also include an additionalloop coil, so that it may transmit or receive predeterminedelectromagnetic waves. When the power transmitter 211 is implementedwith a loop coil, an inductance L of the loop coil is subject to change.It will be understood by those of ordinary skill in the art that thepower transmitter 211 has no limit as long as it is capable oftransmitting and receiving electromagnetic waves.

The controller 212 controls the overall operation of the wireless powertransmitter 200, e.g., using an algorithm, program, or application,which is read out from a memory (not shown). The controller 212 may beimplemented as a Central Processing Unit (CPU), a microprocessor, aminicomputer, etc.

The communication unit 213 communicates with the communication unit 253in the wireless power receiver 250 using Near Field Communication (NFC),Zigbee, Infrared Data Association (IrDA), Visible Light Communication(VLC), Bluetooth, Bluetooth Low Energy (BLE), etc. Additionally, thecommunication unit 213 may perform communication using the Zigbeecommunication scheme or the BLE scheme defined in the IEEE 802.15.4standard. In addition, the communication unit 213 may use a CarrierSense Multiple Access/Collision Avoidance (CSMA/CA) algorithm.

The communication unit 213 transmits signals associated with informationabout the wireless power transmitter 200. For example, the communicationunit 213 may unicast, multicast, or broadcast the signals.

Table 1 below illustrates a data structure of a signal transmitted fromthe wireless power transmitter 200, e.g., at stated periods, accordingto an embodiment of the present invention.

TABLE 1 RX to Report frame protocol sequence network (schedule Numbertype version number ID mask) Reserved of Rx Notice 4 bits 1 Byte 1 Byte1 Byte 5 bits 3 bits

In Table 1, the ‘frame type’ field, which indicates a type of thesignal, indicates that the signal is a Notice signal. Further, the‘protocol version’ field, which indicates a type of a communicationprotocol, is allocated, e.g., 4 bits, and the ‘sequence number’ field,which indicates a sequential order of the signal, may be allocated,e.g., 1 byte. The sequence number increases, e.g., in response to atransmission/reception step of the signal.

The ‘network ID’ field, which indicates a network ID of the wirelesspower transmitter 200, may be allocated, e.g., 1 byte, and the ‘Rx toReport (schedule mask)’ field, which indicates wireless power receiversthat will make a report to the wireless power transmitter 200, may beallocated, e.g., 1 byte.

Table 2 below illustrates an example of an ‘Rx to Report (schedulemask)’ field according to an embodiment of the present invention.

TABLE 2 Rx to Report (schedule mask) Rx1 Rx2 Rx3 Rx4 Rx5 Rx6 Rx7 Rx8 1 00 0 0 1 1 1

In Table 2, Rx1 to Rx8 correspond to first to eighth wireless powerreceivers, respectively. Based on Table 2, a wireless power receiver,whose schedule mask number is represented as ‘1’, i.e., Rx1, Rx6, Rx7,and Rx8, may make a report.

In Table 1, the ‘Reserved’ field, which is reserved for future use, isallocated, e.g., 5 bits, and the ‘Number of Rx’ field, which indicates anumber of wireless power receivers adjacent to the wireless powertransmitter 200, is allocated, e.g., 3 bits.

The signal in the form of the frame in Table 1 may be implemented suchthat it is allocated to Wireless Power Transmission (WPT) in the IEEE802.15.4 data structure.

Table 3 illustrates the IEEE 802.15.4 data structure.

TABLE 3 Preamble SFD Frame Length WPT CRC16

As shown in Table 3, the IEEE 802.15.4 data structure includes‘Preamble’, ‘Start Frame Delimiter (SFD), ‘Frame Length’, ‘WPT’, and‘Cyclic Redundancy Check (CRC)16’ fields. Further, the data structureshown in Table 1 may be included in the WPT field of Table 3.

The communication unit 213 receives power information from the wirelesspower receiver 250. The power information may include at least one of acapacity of the wireless power receiver 250, a battery level, a chargingcount, usage, a battery capacity, and a battery percentage. Thecommunication unit 213 transmits a charging function control signal forcontrolling the charging function of the wireless power receiver 250.For example, the charging function control signal may enable or disablethe charging function by controlling the power receiver 251 in thespecific wireless power receiver 250.

The communication unit 213 also receives signals from other wirelesspower transmitters (not shown). For example, the communication unit 213may receive a Notice signal in the form of Table 1 from another wirelesspower transmitter.

Although FIG. 2A illustrates the power transmitter 211 and thecommunication unit 213 in different hardware structures, the powertransmitter 211 and the communication unit 213 may also be configured ina single hardware structure.

The wireless power transmitter 200 and the wireless power receiver 250exchange various signals. In accordance with an embodiment of thepresent invention, using this capability, a charging process is providedby joining the wireless power receiver 250 to a wireless power networkmanaged by the wireless power transmitter 200.

FIG. 2B is a block diagram illustrating a wireless power receiveraccording to an embodiment of the present invention.

Referring to FIG. 2B, the wireless power receiver 250 includes a powerreceiver 251, a controller 252, a communication unit 253, a rectifier254, a DC/DC converter 255, a switching unit 256, and a charging unit257. Because a description of the power receiver 251, the controller252, and the communication unit 253 has already been provided inrelation to FIG. 2A, a repetitive description will be omitted here.

The rectifier 254, e.g., a bridge diode, rectifies the wireless powerreceived from the power receiver 251 in the form of DC power. The DC/DCconverter 255 converts the rectified power by a predetermined gain. Forexample, the DC/DC converter 255 converts the rectified power so that avoltage at its output terminal 259 is 5V. The possible minimum andmaximum values of the voltage applied to a front end 258 of the DC/DCconverter 255 may be set in advance, and information about these valuesmay be recorded in an ‘Input Voltage MIN’ field and an ‘Input VoltageMAX’ field of a Request Join signal, respectively, as will be describedin more detail below. In addition, a rated voltage value and a ratedcurrent value at the rear end 259 of the DC/DC converter 255 may bewritten in a ‘Typical Output Voltage’ field and a ‘Typical OutputCurrent’ field of the Request Join signal.

The switching unit 256 connects the DC/DC converter 255 to the chargingunit 257, under control of the controller 252. The charging unit 257stores the converted power received from the DC/DC converter 255, if theswitching unit 256 is in an on-state.

FIG. 3 is a flowchart illustrating a method in wireless powertransmitter and receiver according to an embodiment of the presentinvention.

Referring to FIG. 3, the wireless power transmitter detects an objectlocated near the wireless power transmitter in step S301. For example,upon detecting a change in load, the wireless power transmitterdetermines whether a new object is located near the wireless powertransmitter. Alternatively, the wireless power transmitter may detectnearby objects based on voltage, current, phase, temperature, etc.

In step S303, the wireless power receiver searches for a wireless powertransmitter from which it will receive wireless power in at least onechannel. For example, the wireless power receiver transmits a wirelesspower transmitter search signal to at least one wireless powertransmitter, and selects a wireless power transmitter from which it willreceive wireless power, based on a wireless power transmitter searchresponse signal received in response to the wireless power transmittersearch signal. In addition, the wireless power receiver may form acommunication network with the wireless power transmitter from which itwill receive wireless power.

In step S305, the wireless power receiver joins the wireless powernetwork managed by the wireless power transmitter from which it willreceive wireless power. For example, the wireless power receivertransmits a join request signal (hereinafter referred to as a ‘RequestJoin signal’) to the wireless power transmitter from which it willreceive wireless power, and in response, the wireless power receiverreceives a join response signal (hereinafter referred to as a ‘ResponseJoin signal’) from the wireless power transmitter. The Response Joinsignal may include join permission/prohibition information, which thewireless power receiver uses to determine whether joining the wirelesspower network managed by the wireless power transmitter is permitted ornot.

In step S307, the wireless power receiver and the wireless powertransmitter enter a standby state, wherein the wireless powertransmitter may transmit a command signal to the wireless powerreceiver. The wireless power receiver transmits a report signal or anAcknowledgment (Ack) signal in response to the received command signal.If the command signal includes a charge start command, the wirelesspower receiver may start charging in step S309.

FIG. 4A is a circuit diagram illustrating a wireless power transmitteraccording to an embodiment of the present invention.

Referring to FIG. 4A, the wireless power transmitter includes an inputterminal 401 receiving a driving voltage V_(DD). A first end of a coil402 is connected to the input terminal 401, and a second end of the coil402 is connected to a node 403, to which an end of a Field EffectTransistor (FET) element 404, an end of a coil 406, and an end of acapacitor 405 are connected. The other end of the FET element 404 isgrounded. In addition, the other end of the capacitor 405 is also begrounded. The other end of the coil 406 is connected to a first end of acapacitor 407. A second end of the capacitor 407 is connected to afilter 409, which is connected to an end of a capacitor 410 and an endof a coil 412. The other end of the capacitor 410 is grounded.

The wireless power transmitter measures a load or impedance at the inputterminal 401, in order to detect nearby objects. For example, if a newobject is placed near the wireless power transmitter, an abrupt loadchange is detected. Thus, the wireless power transmitter determines thata new object is placed nearby.

Similarly, the wireless power transmitter measures a load or impedanceat the input terminal 401, in order to detect an object moving away fromthe wireless power transmitter. For example, when the measured loadabruptly decreases, the wireless power transmitter determines that anobject previously placed nearby, has not moved away.

The wireless power transmitter detects the load at the input terminal401, and also at a front end 408 or a rear end 411 of the filter 409.That is, the wireless power transmitter determines the placement of anew nearby object or the absence of an object by detecting the loads atvarious parts.

Alternatively, the wireless power transmitter may determine theplacement of a new nearby object or the absence of an object based on avoltage value or a current value.

FIGS. 4B and 4C are graphs illustrating a current and a voltage,respectively, which are measured in the wireless power transmitter overtime, according to embodiments of the present invention.

In FIG. 4B, a current value measured at one point of the wireless powertransmitter is ‘a’ from the start of the measuring until time t1. Afterthe time t1, the measured current is ‘b’. As can be understood from thegraph of FIG. 4B, the current undergoes an abrupt change from ‘a’ to ‘b’at time t1. Further, by detecting the abrupt change, the wireless powertransmitter may determine the placement of a new nearby object or theabsence of a previous nearby object.

In FIG. 4C, a voltage value measured at one point of the wireless powertransmitter is ‘c’ from the start of the measuring until time t1. Aftert1, the measured voltage value is ‘d’. As is apparent from the graph ofFIG. 4C, the voltage value undergoes an abrupt change from ‘c’ to ‘d’ attime t1. Further, by detecting the abrupt change, the wireless powertransmitter may determine the placement of a new nearby object or theabsence of a previous nearby object.

FIG. 4D is a graph illustrating a temperature measured at one point of awireless power transmitter over the time, according to an embodiment ofthe present invention.

Referring to FIG. 4D, the temperature measured at one point of thewireless power transmitter linearly increases. Specifically, thetemperature measured at one point of the wireless power transmitterincreases with a slope of ‘e’ until a time t1. After time t1, thetemperature increases with a slope of ‘f’. As can be understood fromFIG. 4D, the slope for the increasing temperature undergoes an abruptchange from ‘e’ to ‘f’ at time t1. Further, by detecting the abruptchange, the wireless power transmitter may determine the placement of anew nearby object or the absence of a previous nearby object.

FIG. 4E is a graph illustrating a phase at one point of a wireless powertransmitter according to an embodiment of the present invention.

Referring to FIG. 4E, a voltage 421 and a current 422 at one point ofthe wireless power transmitter do not overlap until a specific time.After the specific time, the voltage 421 and the current 422 maypartially overlap, as the phase at one point of the wireless powertransmitter is changed. As the voltage 421 and the current 422 partiallyoverlap, a power loss may occur. That is, the wireless power transmittermay detect an abrupt phase change by detecting the power loss. Bydetecting the abrupt change, the wireless power transmitter maydetermine the placement of a new nearby object or the absence of aprevious nearby object.

In addition, the wireless power transmitter may determine the proximityof an object using an Infrared (IR) sensor or based on a user input.

FIG. 5 is a timing diagram illustrating load detection and signaltransmission in a wireless power transmitter according to an embodimentof the present invention.

Referring to FIG. 5, a controller (TX MCU) 501 of the wireless powertransmitter determines a channel on which it will perform communication,and a network ID in step S510. For example, the wireless powertransmitter may set any one of IEEE 802.15.4 channels 11, 15, 20, and 24as a communication channel. Further, the wireless power transmitter setsa network ID such that it does not duplicate that of another wirelesspower transmitter 503 in the communication channel.

The controller holds the detection state in steps S502 and S515, andtransmits detection powers 513 and 516 for a valid detection periodt_(det) at a stated detection period of stated detection periods oft_(det) _(_) _(per).

Accordingly, the controller 501 may detect an object in step S511. Thedetection power and the size of the valid detection period aredetermined depending on the minimum power and time that the controller501 uses to determine whether there is a candidate device for wirelesscharging within a valid range by detecting a change in a load value ofits power transmitter, i.e., a resonator. That is, because the candidatedevice, i.e., a metal object, is detected from a change in load of theresonator, the controller 501 minimizes the power consumption in thedetection state by periodically generating a sine wave with a lowvoltage, which has a size capable of detecting a load value of theresonator, for a short time required to detect the load value of theresonator. The detection state is maintained for the valid detectionperiod until a new device is detected.

For example, if a wireless power receiver is placed on or over thewireless power transmitter, the controller 501 detects a change in load,and determines that an object is placed nearby the wireless powertransmitter. For example, the controller 501 detects the abrupt changein load as illustrated in FIG. 4A, or detects an abrupt change invarious other criteria as illustrated in FIGS. 4B to 4E.

In FIG. 5, it is assumed that the controller 501 has not detected anabrupt change. Accordingly, the controller 501 applies the detectionpowers 513 and 516 at stated detection periods, without changes inapplied power.

In addition, a communication unit (TX RF) 502 transmits a Notice signalat stated periods in steps S514 and S517. For example, the Notice signalmay have the data structure shown in Table 1 above.

Another wireless power transmitter 503 using the communication channelreceives the Notice signal transmitted from the communication unit 502.The Notice signal, as described in conjunction with Table 1, mayindicate a network ID of the wireless power transmitter, or indicate aschedule of the wireless power receiver that will perform communicationwith the wireless power transmitter. In addition, the Notice signal istransmitted at stated periods, e.g., every 270 ms, so it may be used asa synchronization signal.

FIGS. 6A and 6B are timing diagrams illustrating a power supplyoperation between a wireless power transmitter and a wireless powerreceiver according to an embodiment of the present invention.

Referring to FIG. 6A, a controller 650 of a wireless power transmitterdetects a change in load by applying detection power 602 at statedperiods in step S601. In addition, a communication unit 660 transmits aNotice signal at stated periods in step S603. In FIG. 6A, the controller650 of the wireless power transmitter does not detect an abrupt changein load in step S601.

In step S604, a user 695 places a wireless power receiver near thewireless power transmitter.

In step S607, the controller 650 re-applies detection power, after thepreset period, and detects an abrupt change in load, caused by theplacing in step S604. If a device is detected within a valid detectionperiod, the controller 650 applies driving power (or registration power)P_(reg), which is greater than the detection power 602 by a value 608.

The driving power drives a controller 690 of the wireless powerreceiver.

Accordingly, the controller 690 is driven (or powered on) in step S605,and initializes a communication unit 680 in step S606. The controller650 determines the presence of the wireless power receiver depending onthe presence of a pulse initiated by the controller 690. The controller650 may update the wireless power receiver, the presence of which isdetermined by the controller 650, in a device control table.

FIG. 11 illustrates an example of a device control table according to anembodiment of the present invention.

Referring to FIG. 11, the device control table is used to manage eachwireless power receiver's session ID, company ID, product ID, loadcharacteristic, current characteristic, voltage characteristic,efficiency characteristic, current status, a voltage at a front end of aDC/DC converter of the wireless power receiver, a voltage at a rear endof the DC/DC converter of the wireless power receiver, and a current atthe rear end of the DC/DC converter of the wireless power receiver. Thecurrent status indicates whether the wireless power receiver is in thestandby state after being fully charged, whether the wireless powerreceiver is in the standby state due to the lack of charging power,whether the wireless power receiver is being charged in a ConstantVoltage (CV) mode, or whether the wireless power receiver is beingcharged in a Constant Current (CC) mode.

Referring again to FIG. 6A, the communication unit 680 uses a secondchannel under control of the controller 690. In the example of FIG. 6A,the second channel is used by another wireless power transmitter 670,and is different from the channel used by the communication unit 660.Accordingly, the channel used by the communication unit 660 will bereferred to as “a first channel”.

The order in which the controller 690 determines a search channel may beset in advance, e.g., using IEEE 802.15.4 channels 11, 24, 15 and 20.Further, the initial search channel searched by the controller 690 maybe determined at random.

In step S610, the communication unit 680 transmits a wireless powertransmitter search signal in the second channel. For example, thewireless power transmitter search signal, i.e., a Search signal, mayhave a data structure as shown in Table 4.

TABLE 4 Frame Protocol Sequence Company Product Type Version Number IDID Impedance Class Search 4 bit 1 Byte 1 Byte 4 Byte 4 bit 4 bit

In Table 4, ‘frame type’, which indicates a type of the signal,indicates that the signal is a Search signal. Further, the ‘protocolversion’ field, which indicates a type of a communication protocol, isallocated, e.g., 4 bits, and the ‘sequence number’ field, whichindicates a sequence order of the signal, is allocated, e.g., 1 byte.For example, the sequence number increases, for example, in response toa transmission/reception step of the signal. That is, if the sequencenumber of the Notice signal in Table 1 is 1, the sequence number of theSearch signal in Table 4 is 2.

The ‘Company ID’ field, which indicates manufacturer information for thewireless power receiver, is allocated, e.g., 1 byte, the ‘Product ID’field, which indicates product information for the wireless powerreceiver, e.g., serial number information of the wireless power receivermay be written in this field, is allocated, e.g., 4 bytes, the‘Impedance’ field, which indicates impedance information for thewireless power receiver, is allocated, e.g., 4 bits, and the ‘class’field, which indicates rated power information for the wireless powerreceiver, is allocated, e.g., 4 bits.

In FIG. 6A, three wireless power transmitters use the second channel, byway of example. In steps S611, S613, and S615, respectively, the threewireless power transmitters 670 transmit a wireless power transmittersearch response signal to the communication unit 680, in response to thewireless power transmitter search signal.

The wireless power transmitter search response signal, i.e., a ResponseSearch signal, may have a data structure as shown in Table 5.

TABLE 5 Frame Type Reserved Sequence Number Network ID Response Search 4bit 1 Byte 1 Byte

In Table 5, ‘frame type’, which indicates a type of the signal,indicates that the signal is a Response Search signal. The ‘Reserved’field, which is reserved for use, is allocated, e.g., 4 bits, and the‘sequence number’ field, which indicates a sequential order of thesignal, is allocated, e.g., 1 byte. The sequence number increases, forexample, in response to a transmission/reception step of the signal. The‘network ID’ field, which indicates a network ID of the wireless powertransmitter, is allocated, e.g., 1 byte.

Based on the wireless power transmitter search response signal receivedon the second channel, the controller 690 identifies channel informationand network ID information for each of the three wireless powertransmitters 670 that use the second channel, in steps S612, S614, andS616. In addition, the controller 690 stores the identified channelinformation and network ID information, and Received Signal StrengthIndication (RSSI) strength for each channel, in step S617.

In step S618, the communication unit 680 transmits a Search signal. Uponfailure to receive a Search Response signal to the Search signal, thecommunication unit 680 transmits a Search signal twice more in stepsS619 and S620. If the communication unit 680 fails to receive a SearchResponse signal to the Search signal, even after transmitting the Searchsignal three times, the controller 690 changes or switches the searchchannel to another channel.

In FIG. 6A, the controller 690 changes the search channel to the firstchannel, by way of example.

The communication unit 680 transmits a Search signal using the firstchannel in step S621. The communication unit 660 receives the Searchsignal, and the controller 650 updates the device control tableillustrated in FIG. 11, based on the Search signal in step S622. Inaddition, the controller 650 generates a Search Response signalcorresponding to the Search signal.

The communication unit 660 transmits the generated Search Responsesignal to the communication unit 680 in step S623.

Based on the Search Response signal received on the first channel, thecontroller 690 identifies channel information and network ID informationof the wireless power transmitter that uses the first channel in stepS624. In addition, the controller 690 may store the identified channelinformation and network ID information, and RSSI strength for eachchannel. The communication unit 680 transmits the Search signal threemore times in steps S625, S626, and S627.

Thereafter, the wireless power receiver determines a communicationchannel on which it will perform communication, and a wireless powertransmitter from which it will receive wireless power, in step S628.That is, based on the stored channel information and RSSI information,the wireless power receiver determines the communication channel and thewireless power transmitter from which it will receive wireless power.For example, the wireless power receiver may determine a channel with aminimum RSSI value as a communication channel. Thereafter, thecommunication unit 680 of the wireless power receiver forms a pairingwith the communication unit 660.

Thereafter, the wireless power transmitter and receiver enter into ajoined state.

In step S629, the wireless power receiver generates a Request Joinsignal based on information about the determined communication channeland the determined wireless power transmitter from which it will receivewireless power. The communication unit 80 transmits the generatedRequest Join signal to the communication unit 660 in step S630.

For example, the Request Join signal has a data structure as shown inTable 6.

TABLE 6 Input Input Typical Typical Frame Sequence Network ProductVoltage Voltage Output Output Type Reserved Number ID ID MIN MAX VoltageCurrent Request 4 bit 1 Byte 1 Byte 4 Byte 1 Byte 1 Byte 1 Byte 1 Bytejoin

In Table 6, the ‘frame type’, which indicates a type of the signal,indicates that the signal is a Request Join signal. Additionally, the‘Reserved’ field, which is reserved for future use, is allocated, e.g.,4 bits, and the ‘sequence number’ field, which indicates a sequentialorder of the signal, is allocated, e.g., 1 byte. The sequence numberincreases, for example, in response to a transmission/reception step ofthe signal.

The ‘network ID’ field, which indicates a network ID of the wirelesspower transmitter, is allocated, e.g., 1 byte, and the ‘Product ID’field, which indicates product information for the wireless powerreceiver, e.g., serial number information of the wireless powerreceiver, is allocated, e.g., 4 bytes. The ‘Input Voltage MIN’ field,which indicates a minimum voltage value applied to a front end of aDC/DC inverter (not shown) of the wireless power receiver, is allocated,e.g., 1 byte, the ‘Input Voltage MAX’ field, which indicates a maximumvoltage value applied to a rear end of the DC/DC inverter (not shown) ofthe wireless power receiver, is allocated, e.g., 1 byte, the ‘TypicalOutput Voltage’ field, which indicates a rated voltage value applied tothe rear end of the DC/DC inverter (not shown) of the wireless powerreceiver, is allocated, for example, 1 byte, and the ‘Typical OutputCurrent’ field, which indicates a rated current value applied to therear end of the DC/DC inverter (not shown) of the wireless powerreceiver, is allocated, e.g., 1 byte.

Based on the received Request Join signal, in step S630, the controller650 of the wireless power transmitter determines whether to join thewireless power receiver in the wireless power network. The controller650 of the wireless power transmitter may determine whether to join thewireless power receiver in the wireless power network, based on thedevice control table illustrated in FIG. 11. For example, the wirelesspower transmitter may not permit the joining of the wireless powerreceiver, when the wireless power receiver requires a greater amount ofpower than an available amount of power that the wireless powertransmitter may supply.

When the wireless power transmitter determines to join the wirelesspower receiver in the wireless power network, the controller 650allocates a session ID to the wireless power receiver. The controller650 generates a Response Join signal including the session ID or joinpermission/prohibition information. In step S632, the controller 650controls the communication unit 660 to transmit the generated ResponseJoin signal to the communication unit 680 of the wireless powerreceiver.

For example, the Response Join signal has a data structure as shown inTable 7.

TABLE 7 Frame Sequence Network Session Type Reserved Number IDPermission ID Response 4 bit 1 Byte 1 Byte 4 bit 4 bit join

In Table 7, the ‘frame type’, which indicates a type of the signal,indicates that the signal is a Response Join signal. Additionally, the‘Reserved’ field, which is reserved for future use, is allocated, e.g.,4 bits, and the ‘sequence number’ field, which indicates a sequentialorder of the signal, is allocated, e.g., 1 byte. The sequence numberincreases, for example, in response to a transmission/reception step ofthe signal.

The ‘network ID’ field, which indicates a network ID of the wirelesspower transmitter, is allocated, for example, 1 byte, and the‘Permission’ field, which indicates whether the joining of the wirelesspower receiver in the wireless power network is permitted or prohibited,is allocated, e.g., 4 bits. For example, if the ‘Permission’ fieldindicates ‘1’, it indicates that the wireless power receiver haspermission to join, but if the ‘Permission’ field indicates ‘0’, itindicates that the wireless power receiver is prohibited from thejoining. The ‘Session ID’ field indicates a session ID that the wirelesspower transmitter allocates to the wireless power receiver, for controlof the wireless power network. For example, the ‘Session ID’ isallocated 4 bits.

The communication unit 680 of the wireless power receiver may transmitthe Request Join signal until it receives a Response Join signal fromthe communication unit 660 of the wireless power transmitter.

The controller 690 of the wireless power receiver determines whether itis permitted to join, by analyzing the received Response Join signal,and identifies the allocated session ID in step S633.

In step S635, the communication unit 680 transmits an Ack signal to thecommunication unit 660. The communication unit 660 may transmit theResponse Join signal until it receives an Ack signal from thecommunication unit 680. In step S636, the controller 650 identifies theAck signal with the channel and network ID, and registers the wirelesspower receiver in the wireless network in step S637. For example, thecontroller 660 manages the joined wireless power receiver using thedevice control table illustrated in FIG. 11.

In addition, the controller 660 may control the joined wireless powerreceiver to enter the standby state. For example, the controller 660controls the wireless power receiver to stay in the standby state, ifthe charging of the wireless power receiver is completed, or if thetransmit power is not sufficient to charge the capacity of the chargingunit of the wireless power receiver.

In step S638, the controller determines that there is no change in load,by detecting the current load. In step S639, the controller 650increases applied power to charging power for charging. Thecommunication unit 660 of the wireless power transmitter transmits aNotice signal in step S640, indicating a wireless power receiver withwhich it will perform communication, among the wireless power receivers.The controller 660 of the wireless power transmitter indicates thewireless power receiver with which it will perform communication, usingan Rx to Report (schedule mask) field of the Notice signal.

In step S641, the communication unit 660 transmits a command signal tostart charging. Basically, a command signal, i.e., Command signal,indicates a command that the wireless power receiver is to carry out.For example, the Command signal may have a data structure as shown inTable 8.

TABLE 8 Frame Session Sequence Network command Type ID number ID TypeVariable Command 4 bit 1 Byte 1 Byte 4 bit 4 bit

In Table 8, the ‘frame type’, which indicates a type of the signal,indicates that the signal is a Command signal. The ‘Session ID’ fieldindicates a session ID that the wireless power transmitter allocates toeach of wireless power receivers, for control of the wireless powernetwork. For example, the ‘Session ID’ field is allocated 4 bits. The‘sequence number’ field, which indicates a sequential order of thesignal, is allocated, e.g., 1 byte. The sequence number increases, forexample, in response to a transmission/reception step of the signal.

The ‘network ID’ field, which indicates a network ID of the wirelesspower transmitter, is allocated, e.g., 1 byte, the ‘command Type’ field,which indicates a type of the command, is allocated, e.g., 4 bits, andthe ‘Variable’ field, which supplements the Command signal, isallocated, e.g., 4 bits.

The ‘command Type’ field and the ‘Variable’ field may have variousexamples as shown in Table 9.

TABLE 9 command Type Variable Charge start reserved Charge finishreserved Request report CTL level Reset Reset type Channel scan ReservedChannel change channel

In Table 9, ‘Charge start’ is a command to instruct the wireless powerreceiver to start charging, ‘Charge finish’ is a command to instruct thewireless power receiver to finish charging, ‘Request report’ is acommand to instruct the wireless power receiver to transmit a reportsignal, ‘Reset’ is an initialization command, Channel scan’ is a commandto scan channels, and ‘Channel change’ is a command to change acommunication channel.

In step s642, the controller 690 of the wireless power receiver maystart charging based on the Command signal. In step S643, the controller690 of the wireless power receiver starts charging by turning on aswitching unit between a DC/DC converter and a charging unit.

In step S644, the communication unit 680 transmits an Ack signal, and instep S645, the communication unit 660 transmits a Command signal torequest a report. The Command signal is a Command signal with commandType=Request report.

Upon receiving the Command signal transmitted in step S646, thecontroller 690 measures the current power situation in step S647. Instep S648, the controller 690 generates a Report signal including thecurrent power situation information based on the measurement results. Instep S649, the communication unit 680 transmits the generated Reportsignal to the communication unit 660.

The Report signal is a signal for reporting the current status of thewireless power receiver to the wireless power transmitter. For example,the Report signal may have a data structure as shown in Table 10.

TABLE 10 Frame Session Sequence Network Input Output Output Type IDnumber ID Voltage Voltage Current Reserved Report 4 bit 1 Byte 1 Byte 1Byte 1 Byte 1 Byte 1 Byte

In Table 10, the ‘frame type’ field, which indicates a type of thesignal, indicates that the signal is a Report signal. The ‘Session ID’field indicates a session ID that the wireless power transmitterallocates to the wireless power receiver, for control of the wirelesspower network. For example, the ‘Session ID’ field is allocated 4 bits.

Additionally, the ‘sequence number’ field, which indicates a sequentialorder of the signal, is allocated, e.g., 1 byte. The sequence numberincreases, for example, in response to a transmission/reception step ofthe signal.

The ‘network ID’ field, which indicates a network ID of the wirelesspower transmitter, is allocated, e.g., 1 byte, the ‘Input Voltage’field, which indicates a voltage value applied to a front end of a DC/DCinverter (not shown) of the wireless power receiver, is allocated, e.g.,1 byte, the ‘Output Voltage’ field, which indicates a voltage valueapplied to a rear end of the DC/DC inverter (not shown) of the wirelesspower receiver, is allocated, e.g., 1 byte, and the ‘Output Current’field, which indicates a rated current value applied to the rear end ofthe DC/DC inverter (not shown) of the wireless power receiver, isallocated, e.g., 1 byte.

The wireless power transmitter may transmit the Command signal until itreceives a Report signal or an Ack signal from the wireless powerreceiver. If the wireless power transmitter fails to receive a Reportsignal or an Ack signal from a specific wireless power receiver for anallotted time, the wireless power transmitter may retransmit the Commandsignal to the specific wireless power receiver for an extra time.

FIG. 7 is a flowchart illustrating a method in a wireless powertransmitter according to an embodiment of the present invention.

Referring to FIG. 7, the wireless power transmitter periodically outputsdetection power for detecting a change in load in step S701. If a changein the load is not detected (No in step S703), the wireless powertransmitter continues to periodically output the detection power in stepS701. However, if a change in load is detected (Yes in step S703), thewireless power transmitter outputs driving power for communication witha wireless power receiver in step S705. For example, the driving poweris an amount of power capable of driving a controller of the wirelesspower receiver.

In step S707, the wireless power transmitter determines whether a Searchsignal is received within a predetermined period. If no Search signal isreceived within the predetermined period (No in step S707), the wirelesspower transmitter outputs detection power in step S701. However, if aSearch signal is received within the predetermined period (Yes in stepS707), the wireless power transmitter generates and transmits a SearchResponse signal in step S709. In step S711, the wireless powertransmitter receives a Request Join signal in step S711, and in stepS713, generates and transmits a Response Join signal, in response to theRequest Join signal.

FIGS. 8A and 8B are timing diagrams illustrating an operation wherein awireless power receiver fails to join a wireless power network managedby a wireless power transmitter, according to an embodiment of thepresent invention.

Referring to FIG. 8A, a controller 801 of the wireless power transmitterperiodically outputs detection power 812 and performs load detection insteps S811 and S815, and periodically transmits a Notice signal in stepsS813 and S816.

A user 805 places a wireless power receiver on or over the wirelesspower transmitter in step S817, and a controller 801 detects a change inload in step S814. The controller 801 increases applied power to drivingpower by a value 815, and a communication unit 803 of the wireless powerreceiver is initialized by a controller 804 of the wireless powerreceiver in step S818. The communication unit 803 transmits a wirelesspower transmitter search signal and a wireless power transmitter searchresponse signal in another channel, and stores related information insteps S819 to S827.

Additionally, the communication unit 803 transmits a wireless powertransmitter search signal, receives a wireless power transmitter searchresponse signal by changing channels, and stores related information insteps S828 to S830.

The controller 804 determines a wireless power transmitter from which itwill receive wireless power in step S831, and generates a Request Joinsignal in step S832. The communication unit 803 transmits the generatedRequest Join signal to the communication unit 802 in step S833.

The controller 801 permits joining of the wireless power receiver, andallocates a session ID thereto in step S834. The communication unit 802transmits a Response Join signal to the communication unit 803 in stepS835. However, in FIGS. 8A and 8B, the Response Join signal fails to bereceived at the communication unit 803 of the wireless power receiver.

The communication unit 803 retransmits the Request Join signal in stepS836, because it has failed to receive the Response Join signal in stepS835. However, the retransmitted Request Join signal also fails to bereceived at the communication unit 802. The communication unit 803retransmits the Request Join signal in step S837, because it has failedto receive the Response Join signal.

In step S838, the controller 801 permits the joining of the wirelesspower receiver, and allocates a session ID thereto. The communicationunit 802 transmits a Response Join signal to the communication unit 803in step S839.

In step S840, the communication unit 803 transmits an Ack signal for theResponse Join signal to the communication unit 802 in step S840.However, the Ack signal fails to be received at the communication unit802.

The controller 801 notifies of an occurrence of an error in step S841,when it determines that the signal transmission/reception has failedthree times for a registration limit time (or a join limit time)T_(registration) _(_) _(limit). The ‘three times’ is a mere example, andis subject to change.

In accordance with another embodiment of the present invention, thecontroller 801 of the wireless power transmitter may immediately notifythe error, upon a lapse of the registration limit time, regardless ofthe number of the signal transmission/reception failures, in step S841.

For the notification of the error, visual or acoustic indicator devicesmay be used to generate an alert tone or to blink a Light Emitting Diode(LED). Additionally, the occurrence of the error may be output on adisplay (not shown).

The controller 801 determines whether to remove the cause of an error,by load detection in step S842. The notification of the occurrence of anerror may be repeated in step S843, until the wireless power receiver isremoved from the wireless power transmitter.

The controller 801 may determine whether to remove the wireless powerreceiver, based on whether the load has returned to the initial load.

Accordingly, the controller 801 periodically applies the detection power812, and determines in steps S842 and S845 whether the load has returnedto the initial load. When the load returns to the initial load, as theuser 805 removes the wireless power receiver from the wireless powertransmitter in step S844, the controller 801 of the wireless powertransmitter stops the notification of the occurrence of an error.

FIGS. 9A and 9B are timing diagrams illustrating a method fordetermining to remove a wireless power receiver from a wireless powernetwork managed by a wireless power transmitter according to anembodiment of the present invention.

Referring to FIG. 9A, a wireless power transmitter outputs chargingpower 900 to a wireless power receiver. In step S911, a communicationunit 902 of the wireless power transmitter transmits a Notice signal.The wireless power receiver determines whether to perform communication,by identifying an ‘Rx to Report (schedule mask)’ field in the Noticesignal.

A controller 901 of the wireless power transmitter generates a Commandsignal including its session ID information in step S912, and controlsthe communication unit 902 to transmit the Command signal to acommunication unit 903 of the wireless power receiver in step S913. Acontroller 904 of the wireless power receiver analyzes the Commandsignal in step S914, and generates a Report signal including informationabout the current power situation in step S915. The communication unit903 transmits the generated Report signal to the communication unit 902in step S916. The controller 901 performs impedance matching and thelike, based on the received Report signal in step S917.

A user 905 removes the wireless power receiver in step S918. In stepS919, the controller 901 detects a change in load. The communicationunit 902 transmits a Notice signal in step S920, and transmits a Commandsignal in step S921. The communication unit 902 does not receive aReport signal in step S922 due to the removal of the wireless powerreceiver. The communication unit 902 of the wireless power transmittercontinues to transmit the Command signal during one superframe cycle,which is a period where a Notice signal is transmitted, in steps S921and S923. However, the communication unit 902 fails to receive theReport signal in steps S922 and S924.

The controller 901 performs load detection again in step S925, transmitsa Notice signal even during the next one superframe cycle in step S926,and transmits a Command signal in steps S927 and S929. Even during thatcycle, the communication unit 902 fails to receive the Report signal insteps S928 and S930. The controller 901 performs load detection again instep S931, transmits a Notice signal even during the next one superframecycle in step S932, and transmits a Command signal in steps S933 andS935. Even during that cycle, the communication unit 902 of the wirelesspower transmitter fails to receive the Report signal in steps S934 andS936.

If the communication unit 902 fails to receive a Report signal or an Acksignal even during three superframe cycles, the controller 901determines, in step S937, that the wireless power receiver is removed.As a result, the controller 901 reduces the applied power to detectionpower by a value 938.

Thereafter, the controller 901 performs load detection again byperiodically applying detection power in step S939, and thecommunication unit 902 transmits a Notice signal in step S940. Asdescribed above, the wireless power transmitter may reliably determinewhether the wireless power receiver is removed, contributing toprevention of power waste.

FIGS. 10A and 10B are timing diagrams illustrating communication betweena wireless power transmitter and a wireless power receiver according toan embodiment of the present invention. Specifically, FIGS. 10A and 10Bare timing diagrams for a wireless power transmitter and a wirelesspower receiver performing communication based on a BLE scheme.

Referring to FIG. 10A, a controller 1050 of the wireless powertransmitter checks for a change in load by applying detection power 1002at stated periods in step S1001. In addition, a communication unit 1060of the wireless power transmitter transmits a Notice signal at statedperiods in step S1003. In FIG. 10A, the controller 1050 fails to detectan abrupt change in load in step S1001.

In step S1004, a user 1095 places the wireless power receiver on or nearthe wireless power transmitter.

In step S1007, the controller 1050 re-applies detection power after thesuperframe cycle, and detects an abrupt change in load. When a device isdetected within a valid detection period, the controller 1050 appliesdriving power (or registration power) P_(reg), which is greater than thedetection power 1002 by a value 1008. The driving power may be powercapable of driving a controller 1090 of the wireless power receiver.

A controller 1090 of the wireless power receiver is driven (or poweredon) in step S1005, and initializes a communication unit 1080 of thewireless power receiver in step S1006. The controller 1050 determinesthe presence of the wireless power receiver depending on the presence ofa pulse that is initiated by the controller 1090. The controller 1050may update the wireless power receiver, the presence of which isdetermined by the controller 1050, in a device control table.

For example, the device control table manages each wireless powerreceiver's session ID, company ID, product ID, load characteristic,current characteristic, voltage characteristic, efficiencycharacteristic, current status, a voltage at a front end of a DC/DCconverter of the wireless power receiver, a voltage at a rear end of theDC/DC converter of the wireless power receiver, and a current at therear end of the DC/DC converter of the wireless power receiver. Thecurrent status is information indicating whether the wireless powerreceiver is in the standby state after being fully charged, whether thewireless power receiver is in the standby state due to the lack ofcharging power, whether the wireless power receiver is being charged ina CV mode, or whether the wireless power receiver is being charged in aCC mode.

The communication unit 1080 uses a second channel under control of thecontroller 1090. The second channel is a channel used by anotherwireless power transmitter 1070, which is different from the channelused by the communication unit 1060. Accordingly, the channel used bythe communication unit 1060 is called a first channel.

The order, in which the controller 1090 determines a search channel, maybe set in advance, and the initial search channel searched by thecontroller 1090 may be randomly selected from the BLE channels.

The communication unit 1080 transmits a wireless power transmittersearch signal in the second channel in step S1010. The wireless powertransmitter search signal may include device information of the wirelesspower receiver. For example, the device information of a wireless powerreceiver may include an ID of the wireless power receiver andinformation about a device of the wireless power receiver. Theinformation about a device of a wireless power receiver may include atleast one of a company, a serial number, a protocol version, a hardwareversion, and a parameter associated with charging of the wireless powerreceiver.

In FIG. 10A, three wireless power transmitters use the second channel,and each of the three wireless power transmitters 1070 may transmit awireless power transmitter search response signal to the communicationunit 1080 in response to the wireless power transmitter search signal insteps S1011, S1014, and S1017. The communication unit 1080 transmits aresponse signal or an Ack signal to the three wireless powertransmitters 1070 in steps S1013, S1016, and S1019.

The communication unit 1080 transmits a Search signal in steps S1020,S1021, and S1022.

The controller 1090 may change the search channel to the first channel.The communication unit 1080 transmits a Search signal using the firstchannel in step S1023. The communication unit 1060 receives the Searchsignal, and the controller 1050 stores identifier information of thewireless power receiver and an RSSI value in step S1024. The controller1050 compares the stored RSSI with an RSSI threshold in step S1025, anddetermines whether to respond to the Search signal in step S1026.

When the wireless power transmitter determines to respond, thecommunication unit 1060 transmits a Response signal in step S1028. TheResponse signal may include device information of the wireless powertransmitter. The device information of a wireless power transmitter mayinclude an ID of the wireless power transmitter.

The controller 1090 controls the communication unit 1080 of the wirelesspower receiver in step S1032, and the communication unit 1080 transmitsan identifier and device information of the wireless power receiver instep S1029. The controller 1050 receives the identifier and deviceinformation in step S1030, and determines whether to join the wirelesspower receiver in step S1031.

When the wireless power transmitter determines to join the wirelesspower receiver, the communication unit 1060 transmits a Connectionsignal to the communication unit 1080 in step S1033. The Connectionsignal may include information such as a keep-alive period, and anaddress of each of a wireless power transmitter and a wireless powerreceiver. The wireless power receiver determines an ID of the wirelesspower transmitter and parameters, based on the received Connectionsignal in step S1034.

In accordance with an alternative embodiment of the present invention,the communication unit 1060 may form a communication network bytransmitting a Connection signal in step S1033, immediately afterreceiving the Search signal from the wireless power receiver in stepS1023.

The communication unit 1060 transmits a parameter signal ‘TX parameter’of the wireless power transmitter to the communication unit 1080 of thewireless power receiver in step S1035. The parameter signal of awireless power transmitter may include at least one of an identifier ofthe wireless power transmitter, the wireless power receiver'sidentifier, company, serial number, protocol version and hardwareversion, the amount of available charging power of the wireless powertransmitter, the number of wireless power receivers presently beingcharged, the amount of presently charged power, and the amount ofavailable surplus power.

The communication unit 1080 transmits a parameter signal ‘RX parameter’of the wireless power receiver in step S1036. The controller 1050receives parameters of the wireless power receiver in step S1037 anddetermines 0whether to join the wireless power receiver in the wirelesspower network by analyzing the parameters of the wireless power receiverin step S1038. The controller 1050 generates a ‘Permission info’ signalindicating whether to permit the joining, in step S1039, and transmitsthe join permission signal to the communication unit 1080 of thewireless power receiver in step S1040. The subsequent charging processin steps S1041 to S1052 is the same as that in FIGS. 6A and 6B, whichhas already been described above. Accordingly, a repetitive detaileddescription of steps S1041 to S1052 will be omitted here.

As described above, the present invention may reliably perform wirelesscharging based not only on the Zigbee scheme but also on the BLE scheme.

As is apparent from the foregoing description, various embodiments ofthe present invention provide a wireless power transmitter thatdetermines an addition and removal of a wireless power receiver to andfrom a wireless power network managed by the wireless power transmitter.

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for controlling a wireless powertransmitter, the method comprising: periodically outputting, through aresonator of the wireless power transmitter, first power; based on thefirst power, detecting a first load variation, wherein the first loadvariation is caused by placement of a wireless power receiver within acharging area of the wireless power transmitter; in response todetecting the first load variation, outputting, through the resonator ofthe wireless power transmitter, second power; detecting a system errorwhile outputting the second power; based on detecting the system error,providing an indication, stopping the outputting of the second power,and periodically outputting, through the resonator of the wireless powertransmitter, the first power; and based on the first power, detecting asecond load variation, wherein the second load variation is caused byremoval of the wireless power receiver from the charging area of thewireless power transmitter.
 2. The method of claim 1, furthercomprising: detecting a load of the resonator of the wireless powertransmitter; and detecting a variation of the detected load of theresonator of the wireless power transmitter.
 3. The method of claim 2,further comprising: storing a first value of the load of the resonatorbefore the wireless power receiver is placed on the charging area; anddetecting a second value of the load of the resonator when the wirelesspower receiver is placed on the charging area, wherein detecting thevariation of the detected load of the resonator comprises detecting thatthe load of the resonator is changed from the second value to the firstvalue.
 4. The method of claim 3, further comprising: determining that acause of the system error is removed in response to detecting that theload of the resonator is changed from the second value to the firstvalue.
 5. The method of claim 1, wherein the second power is used by thewireless power receiver to communicate with the wireless powertransmitter.
 6. A wireless power transmitter comprising: a resonator;and a controller configured to: control periodically outputting, throughthe resonator of the wireless power transmitter, first power, based onthe first power, detect a first load variation, wherein the first loadvariation is caused by placement of a wireless power receiver within acharging area of the wireless power transmitter, in response todetecting the first load variation, control outputting, through theresonator of the wireless power transmitter, second power, detect asystem error while outputting the second power, based on detecting thesystem error, provide an indication, stop the outputting of the secondpower, and control periodically outputting, through the resonator of thewireless power transmitter, the first power, and based on the firstpower, detect a second load variation, wherein the second load variationis caused by removal of the wireless power receiver from the chargingarea of the wireless power transmitter.
 7. The wireless powertransmitter of claim 6, wherein the controller is further configured to:control storing a first value of a load of the resonator before thewireless power receiver is placed on the charging area, detect a secondvalue of the load of the resonator when the wireless power receiver isplaced on the charging area, and detect that the load of the resonatoris changed from the second value to the first value.
 8. The wirelesspower transmitter of claim 7, wherein the controller is furtherconfigured to determine that a cause of the system error is removed inresponse to detecting that the load of the resonator is changed from thesecond value to the first value.
 9. The wireless power transmitter ofclaim 6, wherein the second power is used by the wireless power receiverto communicate with the wireless power transmitter.
 10. A method forcontrolling a wireless power transmitter, the method comprising:periodically outputting, through a resonator of the wireless powertransmitter, first power; based on the first power, detecting a firstload variation, wherein the first load variation is caused by placementof a wireless power receiver within a charging area of the wirelesspower transmitter; in response to detecting the first load variation,outputting, through the resonator of the wireless power transmitter,second power; detecting a system error while outputting the secondpower; based on detecting the system error, providing an indication,stopping the outputting of the second power, and periodicallyoutputting, through the resonator of the wireless power transmitter, thefirst power; and based on the first power, detecting a second loadvariation, wherein the second load variation indicates that the wirelesspower receiver is removed from the charging area of the wireless powertransmitter.